This invention relates to electric incandescent lamps of the type which provide radiant energy efficiently and more particularly to a structural configuration for this type lamp to improve its operating efficiency.
One type electric incandescent lamp for general illumination employs a refractory metal filament as the light source. Said light source is commonly supported within a hermetically sealed lamp glass envelope by wire inleads with the filament orientation being either horizontal or vertical with respect to the principal lamp axis. Adequate physical support for the incandescent filament in said type lamp is generally provided by connecting the lamp inleads to both ends of the filament although it is known to provide additional intermediate support along the length of said filament.
Lamps of the same general type are also known emitting selectively in both the infrared and visible spectral regions with such lamps providing studio lighting having a daylight color. A representative structural configuration for lamps of this type is disclosed in U.S. Pat. No. 4,588,923, assigned to the assignee of the present invention, and wherein the selective radiant energy distribution from the lamp is achieved with a reflective film deposited on the lamp envelope. As can be noted from the description appearing in said commonly assigned prior art patent, the optical pass-band and the stop-band characteristics selected for said reflective film medium serve to reflect infrared radiation back to the lamp filament. The filament operating efficiency can be increased in this manner for more efficient light output from the lamp since the reflective film is selected so as to still transmit a major portion of the desired visible radiation. The above mentioned patent is specifically incorporated herein by reference, due to the same reflective film characteristics being employed in the present lamp improvement.
For infrared reflective coatings on such type incandescent lamps to be effective it is essential for the reflected energy to be focused back upon the lamp filament. For this optical criteria to be satisfied, it becomes understandably further necessary that the lamp filament be precisely located with respect to the reflective film deposited on the lamp envelope. Now employed filament support means in lamps of this type do not maintain accurate filament orientation in a number of respects. Said now employed filament support means consists of wire loops enveloping the tungsten coil exterior and exerting a spring pressure against the inner wall of the lamp envelope. Understandably, such flexible support means is not only subject to movement during lamp operation along all of the lamp axes but itself requires physical support by the lamp filament if the lamp is burned in a vertical spatial orientation. Moreover, filament support means of this type cannot easily be introduced into the elongated lamp envelope during lamp manufacture and with disengagement or misalignment frequently occurring at this time between such spiral supports and filament coils.
Accordingly, it is a principal object of the invention to provide more reliable filament support means in an electric incandescent lamp emitting selective radiant energy distribution in order to maintain the filament position more precisely along the principal lamp axis.
It is another important object of the present invention to provide a more effective physical engagement between the filament member and the filament support means in said type electric incandescent lamps.
Still another important object of the present invention is to provide structural means whereby the presently improved filament support means can be further secured in place with respect to the lamp envelope wall.
A still further important object of the present invention is to provide improvement filament support means in said type electric incandescent lamp enabling still more reliable lamp manufacture, particularly with high speed automated lamp manufacturing equipment.
These and other objects of the present invention will become more apparent upon consideration of the following description for the present invention.